[INET]: Use port unreachable instead of proto for tunnels

This patch changes GRE and SIT to generate port unreachable instead of
protocol unreachable errors when we can't find a matching tunnel for a
packet.

This removes the ambiguity as to whether the error is caused by no
tunnel being found or by the lack of support for the given tunnel
type.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 9981dcd..ab99beb 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -656,7 +656,7 @@
 		read_unlock(&ipgre_lock);
 		return(0);
 	}
-	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PROT_UNREACH, 0);
+	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
 
 drop:
 	read_unlock(&ipgre_lock);